This invention relates to friction dampers and, more particularly, to friction dampers in which the frictional damping force obtained is controllable.
Most friction dampers of this type provide control of the frictional damping force obtained by selective adjustment of the normal force applied to one or more friction members which rub against one of two or more relatively movable members. This adjustment typically is accomplished by selective wedging of the friction members against one of the movable members by a jack screw, spring or shim which, once set, applies a constant normal force to the friction members
In many applications, however, it is desirable to vary the frictional damping force obtained in relation to a desired environmental parameter. Some automotive suspensions, for example, vary the frictional damping force obtained in relation to the load applied to a strut or to the pressure inside of a gas spring. Certain aircraft landing gear also do so, but in relation to the velocity of movement of an oleo strut. Some of these devices use fluid pressure to actuate the friction members.
The fluid pressure actuated friction dampers most commonly used in such devices include inflatable bladders or folded membranes to control the normal force applied to the friction member or members, and hence the frictional damping force obtained. These tend to be unsatisfactory. The bladder or membrane must be folded back upon itself and therefore requires complex sealing and positioning devices to maintain it in the proper alignment with the friction members.
As the friction members wear away, moreover, this alignment tends to degrade as the bladder or membrane bulges more and more to take up the attendant slack. In extreme cases, the folds can become so misaligned that the fluid seal may be lost. Further, as the fluid pressure increases, so do the chances of a seal failure. This is especially true in those devices which are used with gas springs, since they typically must operate at pressures of 100-125 pounds per square inch (psi).